1. Field
Various embodiments of the present invention relate to a noise cancellation in a complementary metal oxide semiconductor (CMOS) image sensor and, more particularly, to a replica noise generator for generating a replica noise that copies pixel power noise, and a ramp signal generator including the same.
2. Description of the Related Art
In the general column parallel structure of a CMOS image sensor, noise may be caused by the power supply voltage of a comparator, which operates in differential mode, and the noise may be effectively removed through operations in a common mode.
However, since power noise generated from pixels may be contained in the pixel signal and then applied to the readout circuit, the power noise may remain in the pixel data and affect image sensor performance.
The pixel power noise may include power supply noise or ground noise that overlap within a specific circuit. Additionally, the pixel power noise may include various other noises generated in the pixels.
Since the power noise of the pixels may cause horizontal noise in CMOS image sensors, the pixel power noise needs to be suppressed as much as possible.
Thus, it is suggested that the power noise of the pixel be differentially removed from the viewpoint of the comparator by overlapping the power noise of the pixels with the ramp signal, using a voltage overlapping function.
A replica noise generator that generates replica noise, by copying pixel power noise, may be a useful solution to this concern. By copying the pixel power noise and applying it to the ramp signal, the pixel power noise may be removed resulting in improved pixel data.